Dataset Information

(R)-Ketamine exerts antidepressant actions partly via conversion to (2R,6R)-hydroxynorketamine, while causing adverse effects at sub-anaesthetic doses.

ABSTRACT:

Background and purpose

(R)-Ketamine (arketamine) may have utility as a rapidly acting antidepressant. While (R)-ketamine has lower potency than (R,S)-ketamine to inhibit NMDA receptors in vitro, the extent to which (R)-ketamine shares the NMDA receptor-mediated adverse effects of (R,S)-ketamine in vivo has not been fully characterised. Furthermore, (R)-ketamine is metabolised to (2R,6R)-hydroxynorketamine (HNK), which may contribute to its antidepressant-relevant actions.

Experimental approach

Using mice, we compared (R)-ketamine with a deuterated form of the drug (6,6-dideutero-(R)-ketamine, (R)-d₂ -ketamine), which hinders its metabolism to (2R,6R)-HNK, in behavioural tests predicting antidepressant responses. We also examined the actions of intracerebroventricularly infused (2R,6R)-HNK. Further, we quantified putative NMDA receptor inhibition-mediated adverse effects of (R)-ketamine.

Key results

(R)-d₂ -Ketamine was identical to (R)-ketamine in binding to and functionally inhibiting NMDA receptors but hindered (R)-ketamine's metabolism to (2R,6R)-HNK. (R)-Ketamine exerted greater potency than (R)-d₂ -ketamine in several antidepressant-sensitive behavioural measures, consistent with a role of (2R,6R)-HNK in the actions of (R)-ketamine. There were dose-dependent sustained antidepressant-relevant actions of (2R,6R)-HNK following intracerebroventricular administration. (R)-Ketamine exerted NMDA receptor inhibition-mediated behaviours similar to (R,S)-ketamine, including locomotor stimulation, conditioned-place preference, prepulse inhibition deficits, and motor incoordination, with approximately half the potency of the racemic drug.

Conclusions and implications

Metabolism of (R)-ketamine to (2R,6R)-HNK increases the potency of (R)-ketamine to exert antidepressant-relevant actions in mice. Adverse effects of (R)-ketamine require higher doses than those necessary for antidepressant-sensitive behavioural changes in mice. However, our data revealing that (R)-ketamine's adverse effects are elicited at sub-anaesthetic doses indicate a potential risk for sensory dissociation and abuse liability.

SUBMITTER: Zanos P

PROVIDER: S-EPMC8567221 | biostudies-literature | 2019 Jul

REPOSITORIES: biostudies-literature

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Publications

(R)-Ketamine exerts antidepressant actions partly via conversion to (2R,6R)-hydroxynorketamine, while causing adverse effects at sub-anaesthetic doses.

Zanos Panos P Highland Jaclyn N JN Liu Xin X Troppoli Timothy A TA Georgiou Polymnia P Lovett Jacqueline J Morris Patrick J PJ Stewart Brent W BW Thomas Craig J CJ Thompson Scott M SM Moaddel Ruin R Gould Todd D TD

British journal of pharmacology 20190513 14

<h4>Background and purpose</h4>(R)-Ketamine (arketamine) may have utility as a rapidly acting antidepressant. While (R)-ketamine has lower potency than (R,S)-ketamine to inhibit NMDA receptors in vitro, the extent to which (R)-ketamine shares the NMDA receptor-mediated adverse effects of (R,S)-ketamine in vivo has not been fully characterised. Furthermore, (R)-ketamine is metabolised to (2R,6R)-hydroxynorketamine (HNK), which may contribute to its antidepressant-relevant actions.<h4>Experimental ...[more]

PMID: 30941749

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Project description:(R,S)-Ketamine has rapid and sustained antidepressant effects in depressed patients. Although the metabolism of (R,S)-ketamine to (2 R,6 R)-hydroxynorketamine (HNK), a metabolite of (R)-ketamine, has been reported to be essential for its antidepressant effects, recent evidence suggests otherwise. The present study investigated the role of the metabolism of (R)-ketamine to (2 R,6 R)-HNK in the antidepressant actions of (R)-ketamine. Antidepressant effects were evaluated using the forced swimming test in the lipopolysaccharide (LPS)-induced inflammation model of mice and the tail suspension test in naive mice. To prevent the metabolism of (R)-ketamine to (2 R,6 R)-HNK, mice were pretreated with cytochrome P450 (CYP) inhibitors. The concentrations of (R)-ketamine, (R)-norketamine, and (2 R,6 R)-HNK in plasma, brain, and cerebrospinal fluid (CSF) samples were determined using enantioselective liquid chromatography-tandem mass spectrometry. The concentrations of (R)-norketamine and (2 R,6 R)-HNK in plasma, brain, and CSF samples after administration of (R)-norketamine (10 mg/kg) and (2 R,6 R)-HNK (10 mg/kg), respectively, were higher than those generated after administration of (R)-ketamine (10 mg/kg). Nonetheless, while (R)-ketamine attenuated, neither (R)-norketamine nor (2 R,6 R)-HNK significantly altered immobility times of LPS-treated mice. Treatment with CYP inhibitors prior to administration of (R)-ketamine increased the plasma levels of (R)-ketamine, while generation of (2 R,6 R)-HNK was almost completely blocked. (R)-Ketamine exerted the antidepressant effects at a lower dose in the presence of CYP inhibitors than in their absence, which is consistent with exposure levels of (R)-ketamine but not (2 R,6 R)-HNK. These results indicate that metabolism to (2 R,6 R)-HNK is not necessary for the antidepressant effects of (R)-ketamine and that unmetabolized (R)-ketamine itself may be responsible for its antidepressant actions.

Project description:Enhancing stress resilience in at-risk populations could significantly reduce the incidence of stress-related psychiatric disorders. We have previously reported that the administration of (R,S)-ketamine prevents stress-induced depressive-like behavior in male mice, perhaps by altering α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR)-mediated transmission in hippocampal CA3. However, it is still unknown whether metabolites of (R,S)-ketamine can be prophylactic in both sexes. We administered (R,S)-ketamine or its metabolites (2R,6R)-hydroxynorketamine ((2R,6R)-HNK) and (2S,6S)-hydroxynorketamine ((2S,6S)-HNK) at various doses 1 week before one of a number of stressors in male and female 129S6/SvEv mice. Patch clamp electrophysiology was used to determine the effect of prophylactic drug administration on glutamatergic activity in CA3. To examine the interaction between ovarian hormones and stress resilience, female mice also underwent ovariectomy (OVX) surgery and a hormone replacement protocol prior to drug administration. (2S,6S)-HNK and (2R,6R)-HNK protected against distinct stress-induced behaviors in both sexes, with (2S,6S)-HNK attenuating learned fear in male mice, and (2R,6R)-HNK preventing stress-induced depressive-like behavior in both sexes. (R,S)-ketamine and (2R,6R)-HNK, but not (2S,6S)-HNK, attenuated large-amplitude AMPAR-mediated bursts in hippocampal CA3. All three compounds reduced N-methyl-D-aspartate receptor (NMDAR)-mediated currents 1 week after administration. Furthermore, ovarian-derived hormones were necessary for and sufficient to restore (R,S)-ketamine- and (2R,6R)-HNK-mediated prophylaxis in female mice. Our data provide further evidence that resilience-enhancing prophylactics may alter AMPAR-mediated glutamatergic transmission in CA3. Moreover, we show that prophylactics against stress-induced depressive-like behavior can be developed in a sex-specific manner and demonstrate that ovarian hormones are necessary for the prophylactic efficacy of (R,S)-ketamine and (2R,6R)-HNK in female mice.

Dataset Information

(R)-Ketamine exerts antidepressant actions partly via conversion to (2R,6R)-hydroxynorketamine, while causing adverse effects at sub-anaesthetic doses.

Background and purpose

Experimental approach

Key results

Conclusions and implications

Publications

(R)-Ketamine exerts antidepressant actions partly via conversion to (2R,6R)-hydroxynorketamine, while causing adverse effects at sub-anaesthetic doses.

Similar Datasets

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